38
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion. Potassium bromate, potassium bromide, and water were added in the usual proportions. The mixture was then cooled to 5" C., 2.5 cc. of concentrated hydrochloric acid were added, and the flask was immediately set in a refrigerator kept at 5" C. After a stated number of minutes, 10 cc. of 10 per cent potassium iodide were added rapidly, and the flask was let stand in the refrigerator for a further period of time. The solution was then titrated rapidly with 0.1 N thiosulfate, taking as the titer the volume required to cause a disappearance of the iodine-starch color without recurrence of color on standing for at least 5 minutes. The results obtained are shown in Table IV. Apparently, then, p-ethylphenol and 3,4-dimethylphenol can be estimated with reasonable accuracy and fair reproducibility a t 5" C. if the time of contact with the acid bromination solution is around 2 to 3 minutes. p-Benzylphenol requires a time of contact under these conditions of less than 2 minutes. The alkyl groups in 2,6-dimethylphenol, on the other hand, are so reactive toward bromine that considerably more than the theoretical amount of bromine is used u p even a t 5" C. in as little as 15 seconds. Conditions could probably be established under which many reactive substituted phenols could be titrated reasonably accurately by the Koppeschaar method. However, such conditions would undoubtedly vary from phenol to phenol, and would have to be worked out carefully in each case.
Conclusions Phenol itself and phenols which contain substituents in the meta position react with acid bromide-bromate solution, causing quantitative substitution a t the ortho and para positions. Certain phenols which contain secondary or tertiary alkyl groups in the ortho or para position also brominate quantitatively in this manner. Under the same conditions, phenols which contain primary alkyl groups in the ortho or
Vol. 13, No. 1
para positions give results which may be 10 to 150 per cent high, depending on the nature of the substituents. Dihydroxydiphenylmethane also requires somewhat more than the theoretical quantity of bromine solution. Fresh samples of saligenin require almost exactly three moles of bromine. The methylol group behaves as though i t were not present. p,p'-Dihydroxybenzophenone alone, of the phenols examined, reacted with less than (82 per cent of) the calculated quantity of bromination solution. Certain phenols having primary alkyl substituents in the para position can be estimated accurately by bromination at low temperature. The conditions required for quantitative bromination must be worked out for each individual alkylated phenol. Interpretations of the structure and molecular weight of phenolic resins, or related substances, based upon bromination procedure, should be critically reexamined.
Literature Cited (lj (2) (3) (4)
(5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
A4utenriethand Beutel, Archiv. Pharm., 248, 121 (1910). Auwers, Ber., 36, 1883 (1903); 39, 3160 (1906). Auwers and Anselmino, Ibid.,32, 3587 (1899). Auwers and Broicher, Ibid., 32, 3481 (1899). Auwers and Buttner, Ann., 302, 131-52 (1898). Auwers and Daecke, Ber., 32, 3373 (1899). Auwers and Schroter, Ann., 344, 142 (1906). Beukema-Goudsmit, Pharm. Weekblad, 71, 380-97 (1934). Day and Taggart, IND. ESG.CHEM.,20, 545-7 (1928). Harden and Reid, J . Am. Chem. Soc., 54, 4331 (1932). Jarvinen, Z . anal. Chem., 71, 108-17 (1927). Koebner, Angew. Chem., 46, 251 (1933). Koppeschaar, 2. anal. Chem., 15, 233 (1876). Rednian, Weith, and Brock, J. IND.ENG.CHEM.,5, 389-93 (19 13). Zincke and Walter, Ann., 334, 367-85 (1904). Zincke and Wiederhold, Ibid.,320, 202 (1901).
Determining the Maturity of Frozen Peas A Rapid Objective Method F. A. LEE, New York State Agricultural Experiment Station, Geneva, N. 1.
C"'
L SIDERABLE work has been published (2, 3, 4) concerning the determination of the maturity of vegetables by objective methods, mainly for the purpose of establishing methods that are free from the personal element, ever present in the organoleptic method. A large part of this effort was concerned with canned rather than frozen products. This paper presents an objective method for the grading of frozen peas, to be used in place of the one recommended by the Agricultural Marketing Service. It is an improvement over that method in that it is less time-consuming, less tedious to run in the laboratory, and appears to be more accurate. Like other methods that measure maturity, i t does not take into consideration color and appearance defects such as spots and splits. It depends upon the determination of the specific gravity of thawed peas by means of the difference between the weight of the sample in air and the weight in a liquid, in this case a mixture of xylene and carbon tetrachloride, the specific gravity of which is 1.000. Xylene alone can be used, if desired, although the calculations are a little less simple. This is a modification of the method of Kichols and Reed (6) devised for use on prunes, which uses a mixture of xylene and carbon tetrachloride of specific gravity 0.900.
Specific gravity = weight in air X specific gravity of xylene mixture difference of weights in xylene mixture and in air The equipment employed by Nichols and Reed was modified for convenient use with the relatively smaller samples of fresh vegetables-about 110 grams or a little larger. A triple-beam balance weighing to 0.1 gram is very good; it can be supported on a stand or shelf and the basket can be attached to the hook under the pan. The sample basket was made of 16-mesh brass screen 8.125 cm. (3.25 inches) high and 5.625 cm. (2.25 inches) in diameter. The samples of peas are thawed and then drained for 2 minutes before starting the work. The specific gravity can be found as follows: The peas are weighed in air. Their weight in the xylene mixture can be determined by subtracting the weight of the basket in the xylene mixture from that of the peas and basket in this same liquid. The weight in air minus the weight in the xylene mixture gives the difference of weight in this mixture. The data in Table I were determined a t the normal laboratory temperature of 20" C. It is important, hoTT-ever, that the specific gravity of the liquid used remain constant, and i t can be adjusted to this constant value for the prevailing temperature conditions. The data are arranged in the order of specific gravity as determined with corresponding figures for alcohol-insoluble solids, Agricultural Marketing Service maturity rating, and organoleptic rating. The alcohol-
ANALYTICAL EDITION
January 15, 1941
39
TABLEI. DATAON FROZEK PEAS AlcoholAlcoholOrganoleptic Insoluble Organoleptic Insoluble Specific Rating for A. 11.S. Solids, Specific Rating for A. M. S. Solids, Gravity Maturity Test 70 Gravity Maturity Test % 45 9.74 1.075 A46 10.19 1.056 46 8.40 1.075 A45 10.78 1.059 1.059 A46 9.94 1.076 A 45 9.56 1.059 46 9.52 1.076 B 46 9.91 1.077 A 42 10.09 1.059 B+ 45 10.14 46 11.17 1.060 -4 43 9.55 1.077 1.061 A 47 10.42 1,077 45 10.46 1.061 A45 10.83 1.078 B 46 10.43 1.061 . I44 10.14 1.078 B 46 10.96 1.062 A47 9.62 1,080 B 39 12.53 1.080 39 12.13 1.063 A45 9.48 1.064 A 46 9.81 1.080 42 11.09 1.065 A42 11.02 1.080 B 42 11.24 1.081 A--, B+ 46 10.95 1.065 A44 10,oo 40 11.74 1.066 B+ 1.082 B+ 40 12.08 1.068 B 39 14.66 11 , 0 5 1.085" C+ 44 40 10.67 1.085 B 34 12.52 1.071 B+ 1.072 -4 43 10,60 1.086 A46 9.74 1.073 A 45 10.14 1.08W 39 15.12 42 9 . 9 4 35 1 6.65 1.086' 1.073 47 9.96 1.088a B36 11.56 1.074 1.074 B 40 12.74 l .08gn 41 13.40 1.075 A44 10.73 1.08Qa 34 16.20 a Samples removed by brine separator. Some were standards, others substandard rejects.
Specific Gravity 1.0915 1.091 1.091a 1.092a l ,0 9 P 1.092a 1 .094a 1,09W 1.097 1.09sa 1.09sa 1,099'" 1.099a 1,099a 1,099" 1.100a 1.100a 1,100a 1 ,103a 1 ,103a 1,106" 1 . 106a 1.120Q
i-
E+
E-
-
EE-
:+
TABLE11. COMPARATIVE RATINGS Organoleptic Rating for hlaturity
Organoleptic Organoleptio A. 11. S. A. 11.S. Rating for A . 11.S. Rating for Test Test Maturity Test Maturity 47 A 44 A40a C 47 A 44 A39 B 44 39 B47 44 46 39a B46 A 44 B39a C+ 46 -4 43 A 3Sa C 46 A43 A37a C+ 46 A42 A 36a B42 . I 36a B46 *-sB+ 42 36n C+ 46 B+ 4% 36O. C 46 B+ 46 u 42 B 36" C 46 I3 42 B3tja C 46 I3 42a BC 45 A 42" B35Q C 45 A 41a B35a C 45 A41a B35Q C 45 A41a B35" C 45 A415 34 B c+ 340 40 45 C B+ 34a C 45 B+ 40 45 33a B 40 C 450 B 40 20" C+ 0 Samples removed by brine separator. Some were standards, others substandard rejects.
i-
2-
-
E+
6-
E+
insoluble solids n-ere run after first processing the thawed peas in sealed tin cans a t 115' C. (240' F.) for 30 minutes. The cans containing the peas were filled with hot mater before sealing. After cooling and draining, the determinations were run on these samples in the usual manner ( 3 ) . All the samples given the rating of c and C+ and of those given the B - rating ~veremade up of peas that were rejected by the quality separator for freezing as fancy peas, and many for freezing under any condition. ~1~~ organoleptic ratings for maturity can be arranged according to the results of the test of the Agricultural Marketing Service (Table 11). ~n several samples, the organoleptic rating is at, variance with both the specific gravity and the alcohol-insoluble solids, but in most instances the correlation is good. The organoleptic ratings for maturity after Cooking ( I ) , column 2 of Table I, together with the values assigned to them for use in the calculation of the coefficients of correlation are: A = first grade, 46. A- = quality in grade A, 43. A - , B+ = borderline bet'vveen A and B grade, 42. B+ = high qualit,y in grade B,41. B = satisfactory, but llot first grade, 38. B- = low quality in grade B, 35. C + = high quality in C grade, 34. C = not satisfactorv, 33. - Cal&latioi of the coefficientof correlation-&T\-s a value of -0.8168 * 0.0270 for specific gravity with organaleptic tests. The test of the Agricultural Marketing Service, run on the same samples and compared with these same
Organoleptic Rating for A. M. Maturity Test B 45 B44 C 38 C 35 42 40 B42 B36 B42 41 36 C B41 C+ 36 C 36 C 36 B41 CS. 37 C 36 C 35 C 35 C 34 20 33
AlcoholInsoluble
S. Solids,
E-
'+
ET
70
11.91 11.72 15.85 16.76 14.00 15.36 13.58 14.68 12.53 13.45 15.04 13.44 15.73 15.91 16.43 14.03 15.30 16.82 14.43 16.85 17.07 18.12 16.90
organoleptic tests, showed a value of -0.7029 * 0.0411. Jvhen the alcohol-insoluble solids \vere compared jvith the organoleptic tests, the value for the coefficient of correlation was -0.8301 * 0.0252. According t o these results the method known as alcohol-insoluble solids and the specific gravity method described in this paper are about equally good, but the latter method can be run in a considerably shorter period of time. I n making these calculations there was little need to separate the figures as to varieties because Thomas Laxton peas showed for all practical purposes the same values as the peas of the Alderman variety, both of which were used in this study. It is probable that sweet peas of different varieties grown in other parts of the country for commercial freezing would give similar results. The suggested tentative standards for frozen peas, based upon the comparison of the specific gravity values with the organoleptic tests and upon a knowledge of the samples themselves, might be set as follows: Fancy, specific gravity 1.084 and lower; standard, specific gravity 1.085 to 1.094. Samples haying a specific gravity of 1.095 and higher should be considered substandard. These standards can be revised if and Jvhen an extrastandard grade is generally Packed.
Acknowledgment The author wishes to thank L.8.Fenn of the Agricultural Marketing Service, United States Department of Agriculture, and his &S~oCiatesfor running the organoleptic tests and also for grading these samples on the basis of the test of the Agricultural Marketing Service. In addition, he wishes to thank "le Foods Laboratories, S . J., and the Snider Packing Corporation, Rochester, S . Y., for financial assistance, for supplying material used, and for making available several of their plants for this work.
Literature Cited (1) B ~hlildred, ~ vester)& ~ ~ c~rlner , Packer, 32, NO. 2, 47 (1940). ( 2 ) Jodidi, S.L., J . F l a n k l i n ~ n s t .223, , 593 (1937). (3) Kertess, Z. I., Cunner, 80, KO.11, 1 2 (1935). k'.-4gr. Expt. Sta., Tech. Bull. 233 (19%). (4) Kertess, z. I., (5) Nichols, P. F., and Reed, H . lI.,Hilgardia, 6 , 561 (1932). APPROVEDby the director of the S e w York State Agricultural Experiment
r.
Station for publication as J o u r n a l Paper S o . 383. June 3, 1940.
CORRECTIOK. In the article on "Determination of Methionine in Certain Mixtures'' by J. J. Kolb and Gerrit Toennies [IxD. EKG. CHEM., Anal. Ed., 1 2 , 7 2 3 (1940)] the last paragraph on page 724 refers to ~
the summary.
~ I and b sholild l ~not have been printed a5 a part of
